1. Field of the Invention
The present invention relates to a stereophonic device and a stereophonic method and, particularly, to a device and a method of forming stereophonic sound image using sound data that are generated.
2. Prior Art
So far, the same sound data have been fed to a right speaker and to a left speaker to form a stereophonic sound image. The magnitude of the sound level fed to the two speakers is relatively changed over, so that the stereophonic sound image moves.
For example, when the volume of sound of the right speaker becomes smaller than the volume of sound of the left speaker, the stereophonic sound image moves toward the left speaker. Further, when the volume of sound of the left speaker becomes smaller than the volume of sound of the right speaker, the stereophonic sound image moves toward the right speaker.
However, the above stereophonic sound image is simply created by changing the volume of sound, and is not a true stereophonic sound image.
According to the present invention, the generated sound data are subjected to the digital filter operation by a first digital filter means and by a second digital filter means. The first digital filter means and the second digital filter means execute the same operation, the difference being the filter coefficient only that is supplied and, at the same time, the digital filter operation is executed in parallel therewith. The sound data from the first digital filter means and the sound data from the second digital filter means are simultaneously supplied to different sound systems. Therefore, even though the sound data may be the same, the sound systems generate sounds of different quality of tone, and a delicate stereophonic sound image is formed owing to the difference in the quality of tone.
The digital filter operation is executed by one digital filter means. Due to this operation, the tone is diffracted by, or transmits through, the head to form a sound image in the vertical direction for one ear. The digital filter operation is executed by another digital filter means (FIG. 5). Due to this operation, the sound image is formed in the vertical direction for the other ear. Further, the data subjected to the digital filter operation and the data that is not operated are synthesized at a predetermined distribution ratio to form a horizontal or a vertical sound image. When the distribution ratio (A, K, L) is changed, the position of the sound image moves (FIGS. 6, 13, 14 and 9).
Particular sound images in the horizontal direction and in the vertical direction are subjected to the digital filter operation corresponding to both human ears. The results of digital filter operations are weighted and synthesized, and a sound image in the above other direction is formed depending upon the ratio of weighting (FIG. 10). The digital filter means of the above one channel forms counterbalance sound components of the above one channel, which are sent as subtraction components to the other sound system where they are subtracted from the other sound data and are canceled (FIG. 19). Thus, excess sound/tone components, which are not desired for forming a stereophonic sound image, are erased.